1. Field of the Invention
The present invention relates to an image processing apparatus for recording or reproducing information by a probe or probes disposed about one nanometer close to a recording medium, applying the principle of a scanning probe microscope. More particularly, the invention relates to a surface-aligning mechanism between a recording medium substrate and a probe head substrate in such an apparatus.
It should be noted that the information processing apparatus of the present invention includes all apparatus which perform only the recording of information, which perform only the reproduction of information, or which perform both recording and reproduction of information.
2. Related Background Art
There has recently been developed a scanning tunneling microscope (hereinafter referred to as STM), for example as described in U.S. Pat. No. 4,343,993, which permits a surface of conductive material to be observed with a resolution of below a nanometer. Using the STM, the atomic arrangement on a surface of a metal or semiconductor material or the orientation of organic molecules is observed on the scale of an atom or molecule. Also, the STM technology has been expanded to develop an atomic force microscope (hereinafter referred to as AFM) or a near field optical microscope (hereinafter referred to as NFOM) which permits a surface of an insulating material to be observed with the resolution of the same order as that of STM (see U.S. Pat. No. 4,724,318, or European Patent Application Publication No. EP-0112401-A). Then, it was also suggested that, applying the principle of a scanning probe microscope (hereinafter referred to as SPM) such as the STM, the AFM or the NFOM, data be recorded or reproduced in or from a recording medium while keeping a probe close to the recording medium on the scale of an atom or molecule to create a high-density memory (see U.S. Pat. No. 4,575,822, or Japanese Laid-open Patent Application Nos. 63-161552 and 63-161553).
Further, European Patent Application Publication No. EP-0247219-A discloses an apparatus in which a plurality of probes are formed on a semiconductor substrate for the purpose of miniaturization and a recording medium opposing the substrate is displaced to record data therein. In the apparatus, the probes for detecting a tunnel current are provided on respective cantilevers formed by the semiconductor process and the recording medium facing the probes is set on a cylindrical piezoelectric element to record or reproduce data by a circular motion thereof.
In case a multi-probe array head having a plurality of probe electrodes makes access to a recording medium, a probe head substrate and a recording medium substrate must be set parallel to each other. The distance between the two substrates is normally set to 1 to 3, .mu.m. Further, the dispersion of the distance needs to be not more than +0.5 .mu.m. Then, Japanese Patent Application No. 4-84750 discloses an apparatus in which there are plate electrodes for capacitance detection as provided on the probe head substrate and on the recording medium substrate to detect a capacitance therebetween and in which a distance between the two substrates and a tilt thereof are adjusted to make the capacitances equal to each other at a certain value.
In addition, when data is recorded or reproduced by scanning the surface of a recording medium with the probe head, positioning (surface alignment) must be conducted between the probe head and the recording medium in directions in the surface of recording medium. For this, Japanese Patent Application No. 3-293908 discloses an apparatus in which plate electrodes for capacitance detection are provided on the probe head substrate and on the recording medium substrate similarly as in the above apparatus to detect a capacitance therebetween and in which the relative position between the two substrates are adjusted in directions in the surface thereof to maximize the value of capacitance, i.e., to maximize an area of overlap between the plate electrodes in the in-plane directions.
However, the above conventional apparatus, which adjusts the relative position in the in-plane directions between the probe head substrate and the recording medium substrate, has the following problems, because the relative rotation of the two substrates is carried out after the rotation center of the probe head substrate has been aligned by in-plane movement with the rotation center of the recording medium substrate. Even after the rotation center of the probe head substrate is aligned with the rotation center of the recording medium substrate, a fine positional deviation exists in the in-plane directions between both rotation centers and an actual rotation center of a relative rotation driving mechanism. The in-plane positional deviation sometimes causes a positional deviation in the in-plane directions between the rotation center of the probe head substrate and the rotation center of the recording medium substrate during actual driving causing relative rotation. This reduces the accuracy of adjustment of the relative position of the rotation, which often results in lowering the accuracy of adjustment of the relative position in the in-plane directions.
The adjustment of the relative position in the in-plane directions requires at least two pairs of plate electrodes for capacitance detection to define two directions, e.g., the X direction and the Y direction. The plate electrodes may be rectangular or circular. In actual positioning, it is difficult to align the substrates with each other at high accuracy at once. Then, there are often provided plate electrodes for coarse adjustment and plate electrodes for fine adjustment. Therefore, at least four pairs of plate electrodes are necessary for high-accuracy positioning.
Meanwhile, there are a lot of elements formed on the multi-probe array head having a plurality of probe electrodes. FIG. 1 is a perspective view to show a probe unit 9 produced using the semiconductor fabrication process technology. A piezoelectric bimorph cantilever 8, which is a tongue-shaped, finely moving mechanism, is supported at one end on a single crystal silicon substrate 10 and a probe electrode 7 is formed at the free end of the piezoelectric bimorph cantilever 8, thus forming the probe unit 9. The piezoelectric bimorph cantilever 8 has a layered structure, in which an electrode 1, a piezoelectric layer 2, an electrode 3, a piezoelectric layer 4 and an electrode 5 are laminated in this order from the silicon substrate 10 side. An output electrode 6 is provided for each of the electrodes 1, 3, 5. When a voltage is applied through the output electrode 6 to the electrode 1, 3, 5, the piezoelectric layer 2, 4 contracts or expands, whereby the probe electrode 7 can be freely displaced in a direction perpendicular to the surface of silicon substrate 10 (in the Z direction) or in the X and Y directions parallel to the surface of silicon substrate 10. A lot of such probe units 9 are integrated on the silicon substrate 10 to form the multi-probe array head. A part of a drive circuit for the probe units 9 is also formed on the silicon substrate 10.
As described above, many elements are formed in the multi-probe array head, for example seven wiring lines necessary for a single probe unit 9, as shown in FIG. 1. Thus, only the arrangement of wiring lines requires a considerable region on the substrate. In addition to that, additional pairs of plate electrodes and wiring lines therefor are necessary for position detection, which makes the lines even more dense. This can cause cross-talk between the lines. Such noise greatly spoils the reliability of the apparatus when detecting a weak current, such as the tunnel current.